package com.destin.basic.util;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.Lazy;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.stereotype.Service;


/**
 * @author destin
 * @Description Spring的ApplicationContext的持有者, 可以用静态方法的方式获取spring容器中的bean
 */
@Service
@Lazy(false)
public class SpringContextHolder implements ApplicationListener<ContextRefreshedEvent>, DisposableBean {

    private static ApplicationContext context = null;

    private static Logger logger = LoggerFactory.getLogger(SpringContextHolder.class);

    /**
     * 取得存储在静态变量中的ApplicationContext.
     */
    public static ApplicationContext getApplicationContext() {
        return SpringContextHolder.context;
    }

    /**
     * 从静态变量applicationContext中取得Bean, 自动转型为所赋值对象的类型.
     */
    @SuppressWarnings("unchecked")
    public static <T> T getBean(String name) {
        return (T) SpringContextHolder.getApplicationContext().getBean(name);
    }

    /**
     * 从静态变量applicationContext中取得Bean, 自动转型为所赋值对象的类型.
     */
    public static <T> T getBean(Class<T> requiredType) {
        return SpringContextHolder.getApplicationContext().getBean(requiredType);
    }

    /**
     * 清除SpringContextHolder中的ApplicationContext为Null.
     */
    public static void clearHolder() {
        if (logger.isDebugEnabled()) {
            logger.debug("清除SpringContextHolder中的ApplicationContext:" + SpringContextHolder.context);
        }
        SpringContextHolder.context = null;
    }

    /**
     * 实现DisposableBean接口, 在Context关闭时清理静态变量.
     */
    @Override
    public void destroy() throws Exception {
        SpringContextHolder.clearHolder();
    }

    /**
     * 实现ApplicationContextAware接口, 注入Context到静态变量中.
     */
    @Override
    public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {
        logger.debug("注入ApplicationContext到SpringContextHolder:{}", contextRefreshedEvent.getApplicationContext());
        if (context != null) {
            logger.info("SpringContextHolder中的ApplicationContext被覆盖, 原有ApplicationContext为:" + SpringContextHolder.getApplicationContext());
        }
        SpringContextHolder.createHolder(contextRefreshedEvent.getApplicationContext());
    }

    private static synchronized void createHolder(ApplicationContext applicationContext) {
        SpringContextHolder.context = applicationContext;
    }
}
